Describe 802.11 HE Information Elements

0:01[AUDIO LOGO]

0:05Welcome to describe 802.11 high efficiency or HT information

0:09elements.

0:10Well, if you are working your way through this course

0:11sequentially, we took a look at the HT information elements.

0:14We then took a look at VHT information elements.

0:16And now it's time to look at high efficiency,

0:18which came to us with 802.11ax.

0:21Now 802.11ax or Wi-Fi 6, it brought a lot of new

0:24technologies.

0:25It's got the ability to deploy OFDMA, for example.

0:29We have BSS coloring in here now.

0:31And so we've got all of these technologies

0:33that whether they're at the PHY layer or the MAC layer that

0:36are going to define for us new ways of operation.

0:40And so we need to the ability to specify these capabilities.

0:42And so once again, we're going to find

0:44that we have two different types of information elements.

0:46We have the capabilities information element.

0:49And we have the operation information element.

0:51The capabilities information element is interesting.

0:53First and foremost, we're going to find

0:55is we're actually out of IDs, which is a little bit funny.

0:57We had 1 byte in there for information element IDs.

1:01We've been getting closer and closer

1:02to 255, which is the max value with 1 byte.

1:06And we're here.

1:07We're out of IDs.

1:08So we're going to see how exactly we

1:10get around that now with these new information elements.

1:12So that's the first step.

1:14As far as the capabilities are concerned though,

1:16that's going to get divided up into PHY and MAC fields

1:19where we're describing different capabilities at the two

1:21different layers.

1:22Now from there, we'll take a look at the operation elements.

1:25And this is where we're going to see

1:27some of these other concepts come together.

1:29Ultimately, we've got six different fields

1:31inside the operation element, three of which are mandatory.

1:34And we'll take a video to make sure we go

1:36through all of those in depth.

1:37We'll actually pull up the spec as well.

1:39And make sure that we see this because there's

1:41a lot of flags in here.

1:42A little bit more than we probably are going to--

1:45it's going to be more useful to pull up the spec

1:47and see them than it is to draw them all out on the chalkboard.

1:50Let's put it that way.

1:51So we'll pull up the spec and take a look at some

1:52of these different flags.

1:53But then we also have to worry about the three optional fields

1:56afterwards.

1:57One of which is specifying all kinds of information

2:00if we are deploying this into 6 gigahertz.

2:02And so it's interesting because we don't necessarily

2:05expect to get all this information elements depending

2:07on the band.

2:08If I'm in the 6 gigahertz or even the 2.4 gigahertz band,

2:11I don't expect to get VHT because that's only designed

2:14to work with 5 gigahertz.

2:15But with 6 gigahertz and HT--

2:17I'm sorry.

2:18With 802.11ax and HT, we operate on all of the bands,

2:22whether it's 2.4, or 5, or 6.

2:25We can expect to see these information elements regardless

2:28of which band we happen to be scanning in our Wi-Fi networks.

2:30Let's go ahead and dive in and explore

2:32these different information elements.

2:34And hopefully have a little bit of fun doing so.

2:36With that, I will see you in the next video.

0:00[AUDIO LOGO]

0:05Well, we've covered VHT capabilities and VHT

0:08operations.

0:09So it's time for us to elevate our conversation now to Wi-Fi 6

0:13or 802.11ax or ultimately the high efficiency PHY.

0:16Let's dive in.

0:17Well, once again, we are going to start with the capabilities

0:20element.

0:20But before we dive into the details,

0:22we need to keep a few things in mind as it relates to HE.

0:25First of all, even if we're sending HE,

0:27we are going to need to be backward compatible

0:30and talk about the previous technologies.

0:31So we will be sending the HT, VHT, and HE

0:35all at the same time.

0:36Now, keep in mind what we said about VHT only being applicable

0:39to 5 gigahertz.

0:40And that is the case.

0:41But we also are only going to apply HT to 2.4 and 5.

0:47So as we diagram this out, we realize

0:48HE is going to go to all three of the potential bands.

0:51We start to see our alignment here as far as what's

0:54happening within each band.

0:56So in 2.4, we're going to send HT and HE, in 5 gigahertz,

0:59we'll send all, and in 6 gigahertz,

1:01it's only going to be our HE.

1:03And so at that point, we are only

1:05going to send the HE capabilities element, at least

1:08at the time of this video.

1:10I'm sure we're going to find that when Wi-Fi 7 comes out

1:13that we will have a new information element to be

1:16sending at that point.

1:18But for now, within the context of Wi-Fi 6

1:20being the most recent version, this is where we're at.

1:22Now, we also have some bad news that we

1:24need to get out of the way with, which

1:25is that we've always had these element IDs that are included

1:28inside of our elements.

1:30And the element ID is 1 byte in length.

1:33Well, 1 byte gives us 256 values between 0 and 255,

1:37and we've actually exhausted all of these at the time of coming

1:41out with high efficiency.

1:42And so we need a new structure.

1:44And the way we're going to do this is we're

1:47going to use what we call element ID extensions now.

1:50The element ID extension is going

1:52to be used when the element ID is set to 255.

1:56So if the ID is 255, then we will

1:59look for an extension, which is another 1 byte

2:01field after the length.

2:03And so as we start to draw out our element here,

2:06we will start to break this down.

2:07But at the very beginning, we're going to have our ID,

2:10and the ID will be 255.

2:12255 means we want to look here to find out what

2:15the actual ID is at that point.

2:17So we're skipping over the length,

2:19so we need to diagram that.

2:20So we've got the length here.

2:22And our length here is actually going to be variable,

2:25and we'll see why here in a little bit.

2:27Now, next up is another 1 byte field.

2:29This would be the extended ID.

2:31And in our case, the extended ID is

2:33going to be 35 for the HE capabilities element.

2:36So just keep in mind, if we see an ID of 255,

2:39that means that that's not actually the ID.

2:41We need to look at another header

2:43right here to find out what the true ID is,

2:46and that will help us to distinguish the capabilities

2:49element from other elements that are also

2:51using the extended version.

2:52Now, the rest of the element is broken down

2:54into four different subfields.

2:56The first two are going to play off layer 2 and layer 1.

2:59We have the HE MAC capability subfield,

3:03and then we're going to have the HE PHY capability subfield.

3:07Now, the MAC capability subfield is

3:09going to be 6 bytes in length, whereas the PHY is

3:12going to be 11 bytes.

3:13So this is not drawn to scale.

3:14Keep in mind that the PHY capability

3:17is almost twice as long as the MAC capabilities.

3:19The third subfield is going to be where we talk

3:22about our MCS and our NSS set.

3:25And so this is going to feel a little bit familiar after all

3:28of our other conversations regarding listing out the MCS

3:31rates that we support as well as the Number of Spatial Streams,

3:34which is what NSS stands for.

3:35And this is going to be variable in length.

3:37This is either going to be 4 or 8 or possibly 12 bytes,

3:41and we'll see why here in a little bit.

3:43Now, the last subfield is something

3:44we call the PHY Packet Extension or PPE threshold.

3:48And sometimes this is abbreviated as PPET.

3:51But either way, this is going to be variable length.

3:53And so when we consider the fact that this

3:55is variable length as well as our MCS and NSS set,

3:58subfield is variable.

4:00This is why we can't really predict

4:02exactly how long this capabilities

4:04element is going to be.

4:06We'll start off by taking a look at the HE MAC capabilities

4:09information subfield.

4:10This subfield is 6 bytes in length,

4:12which means we have a total of 48 bits in here.

4:14And those 48 bits are divided up among 37 different flags.

4:19This is a whole lot of information inside of this one

4:22subfield, and we're going to be talking about anything

4:24pertaining to the MAC layer of our high efficiency operation.

4:28And so when we look at this, we're

4:30going to see that we've got things such as our target wake

4:33time parameters in here.

4:34We've got our A-MSDU as well as our A-MPDU parameters

4:38in here as well and many other flags.

4:41Now, rather than detailing all of this out on the chalkboard,

4:44let's go and flip over and take a look at the actual spec.

4:47So as we see here, we've got all of these different bits laid

4:49out as far as whether or not we have single bit fields

4:52or subfields such as these first ones relating to HTC as well

4:56as target wake time.

4:58But we've also got multi-bit fields.

5:01So we've got 2 bits for dynamic fragmentation support,

5:03for example.

5:04As we scroll down, we're going to find

5:06that we've got this listed out for all of our 48 bits,

5:10so 0 through 47 down here.

5:12And so there's just so many different flags in here.

5:15But we can open up the spec, for example,

5:17and we can go right to the section

5:19where it describes all of the different flags.

5:22So here we've got them listed out in a block diagram.

5:25But as we scroll down, we can actually

5:26see what exactly each one of these subfields does.

5:30So we mentioned dynamic fragmentation support

5:33that says it indicates the level of dynamic fragmentation,

5:35and then it actually gives us the listing of all four

5:38of the options.

5:40Because remember, that particular subfield

5:41had 2 bits in there, and as a result,

5:44we have four different options here.

5:45Furthermore, when we're going through the spec, which

5:48is something we should probably do when we're studying

5:51for wireless exams to really understand what's happening

5:54from time to time, we can follow this as a hyperlink to say, OK,

5:57well, this is set 1 or set to 1 if the station supports

6:00level 1 dynamic fragmentation.

6:02OK, that doesn't tell me much until I click on this.

6:05And now it tells me a little bit more

6:07about dynamic fragmentation here.

6:09And so from here, we can just go back to where we were.

6:12And we can, again, understand that there are just

6:16a lot of flags in here, and we're not

6:18going to take the time to break them all down,

6:20but it is important for us to understand

6:22that for the most part, what we're talking about here

6:24is anything related to high efficiency that

6:26has to do with layer 2 and not so much with layer 1.

6:30If we want to understand layer 1 parameters,

6:32we're going to have to go into the next subfield.

6:34And in this case, the next subfield

6:36is our PHY capabilities information.

6:39Now, the PHY capabilities information is, once again,

6:4111 bytes in length, and it's going

6:42to include features such as channel width.

6:45That's going to be something that we actually spend

6:47a little bit of time on here.

6:49We'll take a look at that in the spec

6:50here in a moment, as well as our multi-user MIMO configuration.

6:54We've got to worry about our spatial streams,

6:57and transmit beamforming is a big part of this as well.

7:01There are all kinds of parameters in here

7:02that have to do with the physical layer

7:04of our HE operation.

7:06So once again, we have a block diagram

7:08that tells us all of the different subfields that

7:10are within the HE PHY capabilities information field.

7:14So this is 11 bytes in length.

7:16That means 88 bits.

7:17So we have everything from bit 0 here

7:19at the top all the way to the bottom

7:21where we should see bit 87, and that's what we see.

7:24So we do see some reserved bits in here this time.

7:26But either way, this is going to address things

7:29from a layer 1 perspective.

7:31So we do start off with the supported channel width set.

7:33We need to understand whether we support 20 or 40 or 80 or 160

7:37or 80 plus 80 megahertz.

7:39We've also got things in here related to multi-user MIMO.

7:42We've got our single user and multi-user beamformers

7:45and beamformees.

7:46We've talked about that actually with regards to VHT.

7:51And then as we scroll down here, we

7:53do see an important one right here in the middle, bit 55.

7:56This is a single bit that says whether that PPE thresholds

8:00field is present.

8:01That field is not only variable in length.

8:04It could be as low as 0 bytes, meaning

8:05we're not even including it.

8:07And so if this is a zero, this means we're not

8:09including that final field.

8:11But if it's a one, that means that we

8:13can expect to find data there at the end of this information

8:16element.

8:17And so there's all kinds of information

8:20embedded within here.

8:21And once more, if we want to know a little bit

8:23more information in the spec, we can keep scrolling down,

8:26and we do start to see some information here.

8:28Now, this supported channel width set,

8:30this is really interesting when we get to high efficiency

8:33because the interpretation of this field

8:35is going to depend on whether we're in the 2.4 gigahertz band

8:39or in the 5 or 6 gigahertz bands.

8:42And so as we can imagine, 2.4 gigahertz, yeah, it's

8:45not a great idea, but it does support 40 megahertz.

8:48There is enough bandwidth for that,

8:49but there is not enough bandwidth for 80 or 160,

8:52so we don't even see 80 or 160 show up

8:54in this particular section.

8:57So if we're in 2.4 gigahertz, the bits

9:00are not ever going to enable 80 or 160.

9:03Whereas in the 5 gigahertz or 6 gigahertz range, yeah,

9:06now we can actually activate 80 and 160 and that

9:1080 plus 80 configuration.

9:12And from here, once again, we can always

9:14scroll down and continue to look at these different sections

9:18and read and figure out a little bit more information about not

9:21only what they mean, that would be the description field here,

9:24but then also what are we setting our bits to

9:27and what that ends up doing.

9:28So let's get back to the whiteboard

9:30and talk about this third section.

9:31This is going to be where we talk about our MCS data

9:35rates as well as the number of spatial streams.

9:37And this should be pretty familiar to us

9:39at this point, other than we understand there's

9:41a couple of changes here.

9:42For example, we have new data rates that we should address.

9:45But as far as the number of spatial streams

9:47are concerned, well, that hasn't changed.

9:49We can still only support a maximum of eight.

9:51But we do need to specify our MCS rates that we support

9:55on a per spatial stream basis.

9:56So the way we're going to do this

9:58should, again, feel a little familiar.

9:59We are going to have a receive section,

10:01and then we're going to have a transmit section.

10:04The receive section is going to be 2 bytes,

10:06the transmit section is going to be 2 bytes,

10:08and that gives us 16 bits each.

10:10Now, the way we're going to break this down

10:12is we're going to deliver 2 bits to each spatial stream.

10:15So spatial stream 1, for example,

10:17might be designated as 10, spatial stream 2

10:20might be designated as 10.

10:22Maybe we do that for 3 as well, and then for 4,

10:25we designate this as 11.

10:27And so at this point, we just need

10:29to understand what these different values mean.

10:31I mean, what's a 0 mean versus a 1 and a 2 and a 3?

10:34So let's go ahead and diagram these out.

10:36So we've got these rates, and once again, we

10:39have 2 bits to represent the rates that we support.

10:42Now just like before, a 0 is just

10:44going to mean that we support the bare minimum,

10:46and those requirements don't actually

10:48change relative to HT and VHT.

10:51We need to support MCS rates between 0 and 7.

10:55And then from there, though, we do change things

10:58a little bit because again, we've got new rates.

11:00VHT had 10 rates, so we supported between 0 and 9.

11:04HE, however, adds two more, and we support between 0 and 11.

11:08So how are we going to do this when we still only have 2 bits?

11:11Well, the way we do this is we have

11:13a 1 represent a range of rates between 0 and 9,

11:18and then 2 is going to represent the range from 0 to 11.

11:23And so with VHT, we recall that we stepped from 7 to 8 to 9

11:27in this fashion.

11:28But naturally, unless we add more bits to the equation here,

11:32we can't do that.

11:32We're going to have to take larger steps,

11:34and that's exactly what we do.

11:36Now, a 3 is going to mean just like what it did before,

11:38which is to say that we do not support

11:40this particular spatial stream.

11:42So we look at what I listed out over here,

11:44we have a 2, a 2, a 2, and a 3.

11:47And so when we look at our key down here,

11:50we see that ultimately spatial streams 1, 2, and 3 all

11:54support all of the MCS data rates,

11:56whereas spatial stream 4 is not supported.

11:58Now, do keep in mind that I'm going to have to list this out

12:00for all the other spatial streams as well.

12:02So I've got 5, 6, 7, and 8.

12:04And if I don't support spatial stream 4,

12:06then these are probably all unsupported as well.

12:09So each of these is going to be listed as a binary 11, which

12:12is the equivalent of 3.

12:13Now with transmit, I'm going to do the same thing.

12:15I'm going to have to say spatial stream 1 is 10 and then 2 and 3

12:19and 4 and 5 and 6 and 7 and 8.

12:22And this is why we need 2 bytes or 16 bits for both the receive

12:26and the transmit.

12:28And so adding 2 and 2 together, this

12:30is why we see that 4 is an option here for our MCS

12:34and NSS set.

12:35So then we have to ask, well, where does this 8 and 12

12:37come from?

12:38Well, HE actually allows for us to have

12:40a different configuration here for our larger channel sizes.

12:44In other words, we could have a completely different set

12:47for 160 megahertz.

12:49If we do, then we're going to need 4 bytes for this.

12:51We're going to have to list everything out in here

12:53as it pertains to 160 megahertz, assuming that it's

12:56different than what we support on the lower channel

12:59width sizes.

13:00And so that's where we get another 4 bytes

13:02and why we could have 8 bytes here.

13:03But then we do have another one to talk about,

13:05which is that 80 plus 80.

13:07We might have yet another configuration for 80 plus 80,

13:10and that's going to need its own 4 bytes.

13:12So this is where we get 12 from potentially.

13:14So whether it's 4 or 8 or 12, we're doing the same thing.

13:17We're just repeating it either a single time or possibly two

13:20times or maybe even three times.

13:23Now last up is this PPE threshold.

13:25And remember, not only is it variable in length,

13:27but it is actually optional.

13:29We might not even include this inside of our capabilities

13:32element.

13:32If we are going to include it, then there's

13:34that bit here inside of our PHY capabilities information field

13:38that's going to tell us that yes, indeed PPE threshold is

13:41being included.

13:42Now, remember, PPE stands for PHY Packet Extension,

13:45and this has to do with the padding of our HE PPDUs.

13:50The interesting thing about this is

13:51this is defined on a per spatial stream basis.

13:54It can also be defined on a per resource unit basis.

13:57And so this is why it's variable in length,

13:59and therefore we can't really predict exactly how long

14:02this capabilities element is going

14:04to be unless we just outright say that it's not

14:06going to be included.

14:08Now naturally, if a wireless device

14:09is building these capabilities element to

14:11in order to transmit it, at that point,

14:13we could add up R6 and R11 and maybe

14:16just say that we're going to use the same rates for everything.

14:19And so we're just going to have 4 bytes in there.

14:22And so that would add up to 21 bytes in total for our length.

14:25But naturally, we do need to account for the fact

14:27that MCS and NSS set is variable in length

14:29as well as PPE threshold when it comes to the capabilities

14:33element.

14:34So the HE capabilities element is going

14:36to use an extension ID of 35.

14:38And again, the extension ID is an important part of this.

14:41The ID itself is 255 because we've run out of element IDs.

14:45And so we're going to use this concept where if it's 255,

14:47I'm going to pay attention to the field that's

14:49after a length.

14:50And that ID is what's going to be 35.

14:53And keep in mind, that length is variable

14:55with the HE capabilities element.

14:57Now, we have two primary subfields

14:59that we really zeroed in on.

15:01That would be the MAC and the PHY capabilities.

15:03This is where we really talk about all

15:05of the different capabilities that we

15:07might have within the system and really

15:09specifying whether we have them or not.

15:11And we took a look at that through the spec

15:13itself to see that there are just tons and tons of flags

15:16in there.

15:16And so naturally, we shouldn't expect

15:18to have to memorize this for any particular exam

15:20we're hoping to take.

15:22It's really more a matter of, do we

15:23know where to go in reference to this

15:25as well as just how this breaks down

15:27and just understanding that there's a section for MAC

15:29and a section for PHY.

15:30Now the MCS and the NSS set that's very similar to what

15:34we've talked about before.

15:35But naturally, it can also be applied to the channel width,

15:38and this is where it becomes variable in nature,

15:40and we have that optional PPE thresholds

15:43field at the end as well.

15:44I hope that has been informative for you,

15:46and I'd like to thank you for viewing.

0:00[AUDIO LOGO]

0:05Well, the HE operation element is pretty long as well,

0:08and so we're going to break this conversation into two parts.

0:10We're going to start by talking about the mandatory fields that

0:13must be included within the information element,

0:15and there are three of them.

0:16And then we find that there are three other fields that

0:19are going to be optional, and we'll

0:20talk about those in the next video.

0:22Let's go ahead and see how exactly this element breaks

0:24down, and we'll dive into the details of those first three

0:27fields.

0:27So let's start to break this information element down.

0:30First of all, we have our ID.

0:32And just like before with the capabilities element,

0:34this ID is going to be 255, meaning

0:37we're going to have to check for the extension ID here coming

0:39up.

0:40Now, the length is going to be variable in nature once again.

0:43As we mentioned, we've got three mandatory fields

0:45and we have three optional fields.

0:47And so we'll take a look at those here coming up as well.

0:50But for now, we're going to focus in

0:52on the mandatory fields here in this video.

0:53Now, even though it's variable in nature,

0:55we do know that it's going to be a minimum of 6 bytes

0:58and it can be a maximum of 15 bytes

1:00depending on the inclusion of those optional fields.

1:03Now, after this, we have our extension ID.

1:05And our extension ID is going to be 36.

1:08So our capabilities element was 35

1:11and now our operation element is 36.

1:13Now, from here we have six different fields.

1:15And once again, the first three are going to be mandatory.

1:18The first one is going to be called the HE operation

1:21parameters.

1:22And this field is going to be three bytes in length.

1:25As we might imagine from the name,

1:26this field is going to contain a lot of the different options

1:29that we have available to us as far as HE is concerned.

1:32Now, the next field is one byte in length.

1:35And this is going to have to do with BSS color.

1:38We call it BSS color is included in a lot of our messaging

1:42to help us understand whether we are hearing

1:44a message from a station inside our own BSS

1:48or if it's a station from a remote BSS.

1:50And having different colors on our BSS's are

1:52what helps us to identify that.

1:54Now, the next and last mandatory field

1:56is going to be the basic HE MCS and NSS set.

2:00And this is going to be two bytes in length.

2:02Once again, based on the name, this

2:04is going to include the actual operational configuration

2:07for the MCS and NSS set that we just talked about

2:11in the capabilities conversation.

2:13So what's left here?

2:14We've got these three other optional fields

2:16that we might end up seeing.

2:18The first one is going to be called VHT operation

2:21information.

2:23And this is going to have to do with the fact

2:25that sometimes we're sending HE out into a five gigahertz space

2:28without VHT information.

2:30And if that's the case, we're going

2:31to need to include that here.

2:33So this is three bytes if we include it.

2:36It's 0 bytes if we don't.

2:38So there is no variability to this field

2:40or any of the other optional fields.

2:42The next one is an interesting one.

2:44We call this the max cohosted BSS indicator.

2:48And that's going to be one byte in length.

2:50We'll talk about the details of this field here coming up.

2:53Now lastly, if we are sending this into the six gigahertz

2:56space, then we're going to need the field here

2:58at the end, which is six gigahertz operation

3:00information.

3:02So this is going to include information

3:03that we need from a six gigahertz perspective.

3:06And if we do include this, this is five bytes in length.

3:09So we can see here by looking at the mandatory fields, here

3:12these first three, this is where we can say that at a minimum

3:16it has to be six bytes in length because that's

3:18what the first three fields come out to.

3:21Now, these last three fields, these are the optional ones,

3:24and they come out to nine bytes.

3:25Just keep in mind, though, that we

3:27don't have to include all of them or none of them.

3:30We might actually pick and choose.

3:31We might send the six gigahertz out one.

3:34We might send the VHT out another.

3:36And so in the end, it's unlikely we'll ever hit 15 bytes,

3:39especially since VHT is really designed for the five gigahertz

3:42space, and six gigahertz is naturally designed

3:45for the six gigahertz one.

3:46But either way, we understand that this

3:48is the structure of the element, and we

3:51need to understand which of these are mandatory

3:53and which of these are optional.

3:54So let's start by zooming in on the HE operation parameters.

3:58Once again, this is three bytes.

3:59So it's 24 bits.

4:01And we're going to break this down

4:02into eight different subfields.

4:04Now, rather than listing them all out here on the chalkboard,

4:07I'm going to actually pull up the 802.11ax spec.

4:10And this is something that I would

4:12recommend everyone do is to go out to that IEEE

4:14and download this.

4:16This is something that actually at the time of this video,

4:18the IEEE has made several of their key specifications

4:22available for free.

4:23And so you can see if that's still available.

4:25If not, it might come at a small cost.

4:27But either way, if you do want to follow along,

4:29the HE operation element is listed at 9.4.2.249.

4:34And so run a quick search against that number,

4:36and it should pull up the HE operation element.

4:39So let's go and pull up the spec here,

4:41and we do see this 9.4.2.249.

4:43This is where we start to talk about the HE operation element.

4:47In fact, right away we see a block diagram

4:48of the various fields we.

4:50Do see the three mandatory fields here as well as

4:52the three optional fields, and it

4:54does give the indicator of how many bytes are in each.

4:57Now, as we scroll down here, we get a block diagram

4:59of the HE operation parameters field,

5:01which is what we want to break down and start to talk about.

5:04So let's start here with the default PE duration.

5:06This is a duration that ties to our high efficiency

5:09trigger based PPDUs.

5:10And this is going to give us a value that is multiplied

5:13by four microseconds.

5:15So we are given a duration there as far as how exactly

5:18we are to send those PPDUs.

5:21Now once again, when we're reading the spec,

5:23we actually see a small paragraph here

5:24that describes that as well as a hyperlink

5:26that if we want to click on that,

5:28we can go and learn a little bit more information about what

5:31exactly is happening there.

5:32But either way, we're just going to go ahead and move on.

5:34And we're going to talk about target wake time.

5:37This subfield is a single bit.

5:38And this is simply going to tell us whether or not

5:40target wake time is required.

5:42So a 1 means it's required.

5:44A 0 means it is not.

5:45And keep in mind, again, this is an operation element.

5:48And so we're describing the operation of the BSS.

5:50And so stations are going to need to abide by this.

5:54Do they support target wake time when

5:56they're trying to join the BSS or do they not support it?

5:59The next step is this transmit opportunity duration

6:01for the RTS threshold.

6:03This is actually 10 bits in length.

6:05And this is another duration field.

6:07And so this is going to be multiplied by 32 microseconds

6:10based on whatever value is inside of there.

6:12A station that wants to use RTS and CTS has

6:15to transmit for at a minimum, the amount of time

6:17expressed inside of this subfield.

6:20And so if we have a very large amount of time specified,

6:23that means that we can't actually use an RTS in order

6:27to send something unless we have a bunch of information stored

6:30up that we can send.

6:32And so to be clear, this is a minimum threshold, not

6:34a maximum threshold.

6:35We're not saying how much time you can spend.

6:38We're saying if you're going to use

6:39RTS to create a transmit opportunity,

6:42you have to have enough data based on the amount of,

6:45well, really based on this duration

6:46that we've set, the value multiplied by 32 microseconds.

6:50And by the way, if all of these are set to 1 where we have

6:53a 1023 in here, that means that we cannot use RTS at all.

6:58Now, next up we have an important flag here

6:59that's going to tell us whether or not we have

7:02this optional field included.

7:03So I know it's off the screen up there,

7:05but that's the VHT operation information field,

7:08and that's one of the optional ones.

7:10That's why we say it's either 0 or 3 bytes.

7:12In fact, we have another one of these

7:14here, the six gigahertz at the end, the 0 or 5

7:16that we mentioned.

7:17And this bit right here tells us whether that one is included.

7:21Any station receiving this information element

7:24needs to understand which fields are included,

7:26which aren't, and these single bit flags

7:28are how we end up doing that.

7:30Now, we're not quite done yet, because we

7:31have a third optional field up there.

7:34And that's going to be tied to the cohosted BSS flag.

7:37However, this cohosted by this flag

7:39also is going to tell us whether or not we

7:41are using this functionality.

7:43We'll talk about this in a little bit more detail later,

7:45but ultimately what we're saying is

7:47that we can have multiple access points managing a single BSS.

7:52It's a feature we don't talk about very often,

7:54but it's technically possible using high efficiency.

7:57Now, the last one here, this extended range single user,

8:00that is one of our four different PPDU types.

8:03We've talked about this as it relates to high efficiency

8:05throughout the course.

8:06Ultimately what we're saying here is,

8:08can the access point receive extended range

8:11single user PPDUs?

8:13And then at the end here, we have a reserved field.

8:16And so the last six bits inside of our HE operation parameters,

8:21those are simply reserved at least

8:22at the time of this video.

8:23So that is the HE operation parameters field.

8:26Let's go ahead and scroll down and take a look at BSS color.

8:30BSS color is a single byte and so we

8:32don't have a whole lot here, but we'll

8:33go ahead and walk through this.

8:35So remember the concept of BSS color

8:37is that usually I've got non-overlapping cells here

8:40that are running on the same channel.

8:42So let's say we're running channel

8:4344 in each one of these cells.

8:45But naturally, wireless, it goes a lot further than we like

8:49to think and goes well beyond our cell boundaries,

8:51especially when we have a station that's

8:53out here that's connecting in.

8:55Well, in the end, it's not too far away

8:57from the next cell over.

8:59And so we've got a lot of communications that are going

9:01back and forth between these.

9:03And if a station here at the edge

9:05is hearing something coming in from another station

9:09in that BSS, the one that's far away, well, at this point,

9:12it has no choice but to wait because somebody else is

9:15communicating.

9:16But if we have different colors assigned,

9:18and colors are ultimately a numerical value

9:21not an actual color, so if we've got numeric values of 32 and 67

9:26in here, well, at this point I know that because this message

9:30is marked with 67 that I probably don't need to wait,

9:33because that person is communicating closer

9:36to their access point than I am, and chances

9:39are it's not going to cause interference.

9:40So that's the idea of BSS color.

9:43And so as we diagram this out, the first thing

9:45and most important part is the color itself,

9:47which is a six bit field.

9:49And so our colors can range between 0 and 63

9:52based on these six bits.

9:54Now, next we do have the concept of a partial BSS color.

9:57It's an option within the configuration of BSS colors.

10:01And whether or not it's enabled, that particular option

10:04is right here as a single bit flag.

10:05And lastly, we do have this option of BSS color

10:08being disabled.

10:10Keep in mind if it says disabled here,

10:11that means that a 1 means that it's true,

10:14meaning that BSS color is disabled, whereas a 0 is saying

10:17that it is actually enabled.

10:19And so that's it.

10:20That's all that's in the BSS color information field.

10:23Again, it's only a single byte.

10:25So we only had eight bits to worry about.

10:27Now let's look back to the chalkboard

10:28here to see where we're at.

10:30We've got the HE operation parameters covered.

10:32We covered the BSS color.

10:34Let's go and talk about this basic MCS and NSS

10:37for high efficiency.

10:39As we have pointed out a couple of times,

10:40this is an operation element, and so we're no longer

10:43talking about capabilities.

10:44We're talking about how the BSS is actually configured.

10:47At this point, we've in theory got

10:49an access point managing a BSS with a bunch of stations

10:52here inside.

10:54And part of the operation element,

10:56as we've talked about with HT and VHT,

10:58is to let everybody know all of the different MCS

11:01rates that are actually enabled inside of this BSS.

11:04And this is going to be based on the existing stations.

11:08Because if an existing station doesn't

11:10support a particular MCS value, then we're

11:13going to need to avoid using that data rate,

11:16especially if somebody has a broadcast or multicast

11:18message to send out into the wireless space.

11:21Now, it doesn't happen too often.

11:22Most of our communications are unidirectional between

11:25an access point and a station.

11:27But just in case something like that does happen,

11:29everybody needs to know whether certain rates are supported

11:32or not.

11:33And so ultimately, we're going to do here what we've already

11:35done several times.

11:36We're going to take two bytes, which is really 16 bits,

11:39and we're going to divide those up among the spatial streams.

11:42So spatial stream one is going to list out

11:44those four different options.

11:45So maybe spatial stream one is listed as a two here.

11:48Or maybe spatial stream two is listed as a one.

11:51We have less functionality here.

11:53Maybe spatial stream three is listed as a 0

11:56and so on and so forth.

11:58And so we just need to understand what everybody out

12:00there supports.

12:01Now, these values are the same as what we've talked about.

12:040 is going to be between 0 and 7.

12:071 from an HE perspective is going to be between 0 and 9.

12:112 will be 0 to 11.

12:13And 3 means that we are not supporting

12:15this particular spatial stream.

12:17So again, the way that we architect this is very similar.

12:20However, in this case, we're not advertising capability.

12:22The access point isn't saying what it's capable of doing.

12:25It's saying what the BSS is capable of doing

12:27based on the stations that have associated to the access point.

12:31So this HE operation element has an extended ID

12:34of 36, which by the way, means that its element ID is 255.

12:38And then the length is going to range between 6 bytes

12:41and somewhere up towards 15.

12:43Again, we probably aren't ever going to see it hit 15.

12:45But at the same time, we understand

12:47that some of these fields might be included, some of them

12:49might not.

12:50And so it's important for us to recognize

12:51that there are three mandatory fields as well

12:54as three optional fields.

12:55The first three fields are the mandatory ones.

12:57And in that first field, we actually

13:00have bits that tell us whether or not

13:02any of those other fields have been included

13:04in this information element.

13:06And so the last three are the optional fields.

13:09Now, the mandatory fields that we're

13:11talking about, we have the HE parameters to start with,

13:14the operation parameters.

13:15We've got the BSS color.

13:16It's only one byte.

13:17And most of that byte is just providing the BSS color

13:20itself, which is six bits.

13:21And then we have to describe the MCS rates as well

13:23as the number of spatial streams,

13:25and we use our two bits per spatial stream

13:27in order to describe that and broadcast out

13:29what the configuration is for the BSS

13:32based on the stations that have associated.

13:33I hope this has been informative for you,

13:35and I'd like to thank you for viewing.

0:00(light music)

0:05<v ->Alright, we have covered the mandatory fields</v>

0:07that show up inside of the HE operation information element.

0:11Let's go ahead and now unpack those three optional fields

0:13that may or may not be included.

0:15So we've covered those mandatory fields.

0:17Let's dive into these optional ones.

0:19The VHT operational info.

0:21This is an interesting one,

0:23because we've actually already talked about

0:25this specific field.

0:26This field exists inside of the VHT operation element,

0:31and the reason why we're duplicating this

0:33is because there could be a scenario

0:35where we are sending out the HE operation element

0:38and we don't have the VHT operation element.

0:41If we don't have the VHT operation element,

0:43then we're not going to have the VHT operation information

0:46that shows up inside of it.

0:48And so this is the scenario.

0:49We don't have this element,

0:51and therefore we need to include this information here

0:53inside the HE operation element.

0:56So as mentioned, this is three bytes, which is 24 bits.

0:59And if we go back and take a look at the conversation

1:02we had earlier about this field,

1:04we'll find it's the same size and it has the same flags.

1:07This is primarily going to have to do

1:08with our channel configuration.

1:10So we recall we started with channel width.

1:12We had one byte dedicated to this,

1:15and then this is where we have that center frequency zero

1:17and center frequency one concept,

1:20where each of these is going to describe

1:21the center frequency,

1:22especially when we have that 80 plus 80 configuration,

1:25and each one of these is a one byte field.

1:27So this is where we get our three bytes from.

1:29If you want more information,

1:30then be sure to go back and review the video

1:32where we discussed the VHT operation element,

1:34'cause we go into this in much more depth.

1:37Now, next up, we have

1:38this one byte max co-hosted BSSID indicator field.

1:42This is a rather interesting conversation,

1:44because high efficiency allows for us to have this concept

1:47of a co-hosted BSS.

1:50The co-hosted BSS has multiple access points,

1:53but they share a lot of the properties

1:55that normally belong to a single access point,

1:58such as the BSSID.

2:00Now, what this field is saying

2:01is we're listing out the max number of co-hosted BSSIDs

2:05that we can have.

2:06However, this doesn't just follow a straight number,

2:08we're not talking about between zero and 255,

2:11this is actually an exponential number.

2:13And so it follows the formula

2:15where it's two to the power

2:17of whatever value we have in here.

2:19And so keep in mind that this is one byte,

2:22and therefore we would expect

2:23that we could have this between two to the zero

2:25and two to the seventh power.

2:27However, there is a limit of eight on here,

2:30and so I'm not exactly sure why they architected it

2:32the way they did;

2:33however, for the time being,

2:35the maximum value we can have in this field is three.

2:37So technically, it's not zero to seven,

2:39it's going to be zero to three in the exponent,

2:42which is why we can land between one, technically,

2:44to two to the zero power and eight different BSSIDs,

2:49all co-hosting a single BSS.

2:51So last, let's talk about the six gigahertz field,

2:53what we call the six gigahertz operation information.

2:56This field is five bytes in length,

2:58and what we're going to find is it's actually carved up

3:00into five separate one byte subfields.

3:03We'll go through each one of these.

3:04First of all, we are going to list out the primary channel.

3:08The primary channel is simply going to tell us,

3:10well, just what it sounds like,

3:11the primary channel that we're operating on

3:13in this scenario.

3:14And this is pretty straightforward;

3:16we're simply going to list the ID inside of the subfield.

3:19Now, next, we have a subfield called control.

3:22This control subfield actually

3:24has quite a bit going on within it.

3:26First of all,

3:27we have two bits that are dedicated to the channel width.

3:30We're going to specify either a zero,

3:32meaning that it's a 20 megahertz channel,

3:34a one, meaning it's a 40 megahertz channel width,

3:37two is 80, and three is 160,

3:41or possibly that 80 plus 80 configuration.

3:44Next, we're gonna have a flag,

3:45a single bit flag that has to do with duplicate beacons,

3:49whether we're sending duplicate beacons out

3:50across multiple spatial streams.

3:52Then we have three bits dedicated to

3:55what is called the regulatory info.

3:58This provides information about whether we're talking about

4:00indoor or standard operation.

4:02We recall that when we talked about six gigahertz,

4:05we had that low power indoor concept,

4:07we have standard power,

4:09and so we're going to describe what's happening here;

4:11however, keep in mind that this is always going

4:13to be tied back to the regulatory domain.

4:15So for example, in the United States,

4:18if I see a zero in this field,

4:20this means that we're doing low power indoor.

4:22If I see a one in this field,

4:24this means we're doing standard power.

4:26In the United States, as of the time of this video,

4:29these are the only two options that we have available to us.

4:32We may recall that other regulatory domains have

4:34a very low power option,

4:36and so these bits are going to mean something different,

4:39depending on the regulatory domain

4:41that we're operating under.

4:43Now, an important part about all of this

4:45is we don't actually provide the domain inside

4:47of these three bits;

4:49the domain is provided in a different information element.

4:52And so we have to reference that other information element

4:54to figure out what domain we're in

4:56in order to understand what these bits are.

4:58If I find out I'm in the US and there's a one in this field,

5:00I know it stands for standard power,

5:02but if I happen to be operating in a different country,

5:04a one might mean something completely different.

5:07And so this is going to, again,

5:09be relative to the regulatory domain

5:12that I'm operating within.

5:13Now, lastly, there are two more bits in here,

5:15but those bits are reserved.

5:16Next, let me clear up part of the chalkboard here

5:18so we can continue this conversation,

5:20'cause we still have three more one byte subfields to cover.

5:23The next one up is going to actually feel pretty familiar,

5:26we just listed this concept out.

5:28We have the channel center frequency segment zero,

5:31which would be our third subfield within

5:33this six gigahertz operation information field,

5:36and then fourth up we have

5:38the channel center frequency segment one.

5:41So once again, this is going to provide the center frequency

5:43for the channel that is in use.

5:46The first one, segment zero,

5:47this is going to be the primary channel.

5:49And if we're talking about a 160 megahertz or an 80 plus 80,

5:54this is actually going to be

5:55the primary 80 megahertz channel, in this case.

5:59Now, if we do have one of these larger channel widths,

6:01we need to know

6:02what the secondary 80 megahertz center frequency is,

6:05and that's what this down here is for.

6:07And so this is especially going

6:08to be relevant with 80 plus 80,

6:09'cause we need to know where that secondary channel is,

6:12and so that information is carried in here.

6:15Now, lastly, there's only one more subfield to talk about,

6:18and it is number five;

6:19it is the minimum data rate.

6:21This one is fairly straightforward.

6:22It is going to express the minimum data rate supported

6:25by this particular device,

6:26and this is going to be expressed in megabits per second.

6:30And so that's where we get our five bytes from.

6:32And as you can imagine,

6:34the six gigahertz operational info field,

6:36this is only going to be included

6:37if we're transmitting into the six gigahertz space.

6:40So this concludes our conversation around

6:42the AT operation element.

6:44The operation element has the three mandatory fields

6:46that we just talked about before,

6:48but now here we've talked about the optional field.

6:50So we have VHT operation,

6:51we have the co-hosted BSSID,

6:53the max number of those,

6:56and then the six gigahertz operation information.

6:58So all three of those,

7:00again, in total, we can add up to nine bytes in here,

7:03but it's, we're not gonna find a situation

7:05where we're using all three at once.

7:07Either way, the VHT operation field,

7:09keep in mind that that's tied back to whether

7:11we're including the VHT operation information element.

7:14If we are not, then we need to actually include some

7:17of that information in our transmissions,

7:19and so this operation field

7:22is actually going to reflect exactly how

7:24the previous field is architected,

7:25and it includes the same information, like we discussed.

7:28Now, we talked about the six gigahertz as well quite a bit.

7:32If we're in the six gigahertz band,

7:34we're going to send it out.

7:34It's got all of our channel information in there,

7:36it's got a whole bunch of other important pieces,

7:39like the channel ID and such

7:41that are going to pertain to six gigahertz operation.

7:44I hope this has been informative for you,

7:45and I'd like to thank you for viewing.

0:00[AUDIO LOGO]

0:05We have reached the end of another skill,

0:07it's time to review what we've learned with a quiz.

0:09First up out of four questions.

0:11What can cause the HE-MCS and NSS

0:14Set to consume eight or 12 bytes relative to the four bytes

0:18that it normally would consume otherwise?

0:25So WPA has nothing to do with this.

0:28Yeah, saying more than four spatial streams,

0:30but we are already accounting for all eight

0:32of those spatial streams in the four bytes.

0:34And so that's not going to affect things either.

0:36C is going to be our answer here.

0:38Remember four bytes is going to be

0:40used assuming that all of our channel

0:42would support the exact same in data rates.

0:45However, our 160 megahertz channels

0:47might actually support different data rates.

0:49And so at this point, we would add four bytes, where

0:52the second four bytes addresses 160,

0:54and the original four bytes now address the 20, 40,

0:57and 80 megahertz.

0:59Now that said, we might actually need

1:01another four byte set to account for the 80 plus 80

1:04configuration.

1:05At this point, we would have a total of 12 bytes in here

1:08because we'd have three different configurations.

1:12So these are only required if we have different configurations

1:15at the different channel widths.

1:16This is why it could truly be four bytes originally,

1:19or it could be eight, or it could be 12,

1:21depending on our needs.

1:22Either way, C is going to be our answer.

1:25Question two.

1:26What is the length of each of these fields

1:27and the HE operation element?

1:35So we should definitely have a sense of how this information

1:37element is constructed.

1:39Now, I did us the favor of listing them

1:41in order from start to finish.

1:43And so all we really need to do is remember

1:45how long each of these can be.

1:46So the HE Operation parameters, this is a three-byte field

1:50and it's going to have a lot of the various flags in there

1:52that pertain to operation outside of the other corner

1:56cases like, BSS, and MCS, and number of spacial streams.

1:59Now the BSS Color Information, this is just a single byte.

2:02And the BSS color is six bits of those eight bits.

2:05And so for the most part, we don't

2:07need a whole lot of information around BSS color.

2:09Next up we have this MCS and number of spatial streams set.

2:13This is classically going to be two bytes from an operations

2:16perspective because we don't need

2:17to list receive and transmit, and we

2:19don't need to list this for different channels potentially.

2:22And as a result, we really only need 16 bits

2:24in total, which is the two bytes.

2:27VHT Operation Information, this again is just a repeat of--

2:30when we covered this with VHT, and so this

2:33is going to be a three byte field, in the way

2:35that we discussed.

2:36The Max Co-Hosted BSSID Indicator,

2:39this is only a single-byte.

2:40We're not going to need a whole lot of information in here.

2:43In fact, we can't even use the entire range of that byte

2:45because we recall that we're restricted

2:47in the amount of the number that we can specify here.

2:51Now lastly, the 6 Gigahertz.

2:52This is actually a big one.

2:53This is the biggest one of all of these,

2:55we have five bytes here.

2:57And remember this consists of five

2:58separate one-byte subfields.

3:00So we didn't have this memorize, that's probably not the biggest

3:04deal.

3:04But at the same time, again, we should

3:06have a sense of where all the information is going when

3:09it comes to how especially one of these information elements

3:12is constructed.

3:13Question three.

3:14When is the VHT Operation Information field

3:17included in the HE Operation Element?

3:25Well, this one's pretty straightforward.

3:26Remember we have a situation potentially,

3:29where the HE Operation element is included,

3:31and the VHT is not.

3:33If that's the case, then we need to include

3:35of some of this information at least inside of our HE

3:38Operation element.

3:39And so, A is the answer here, it's

3:41when the VHT Operation element at least is missing.

3:45And at that point, again, we're going

3:47to import as it were one of these particular fields.

3:51So this field, the VHT Operation Information field

3:54that shows up both in the VHT Operation element,

3:57but also in our HE Operation element as an optional field,

4:01in case we need it.

4:03Last question.

4:04And it's a little bit of a review

4:06of the last several skills.

4:07What are the IDs used for each of these information elements?

4:16So every one of our information elements

4:18has what we call an "element ID."

4:20The element ID is going to tell us what type of element

4:23this is, because we don't have a solid structure out there

4:26for which elements should be included, in which order.

4:29So starting all the way at the beginning with HT Capabilities,

4:32this was 45 as an ID.

4:35In HT Operation, it's unfortunately not sequential,

4:38this was a 61.

4:39So those are two of the harder ones

4:41to remember, because the other ones actually

4:42do build on each other.

4:43For example VHT Capabilities, this is 191.

4:47And VHT Operation is 192.

4:49Now lastly, when it comes to HE Capabilities,

4:52we actually go smaller here.

4:53We start with 35 for capabilities,

4:55and 36 for operation.

4:57Just keep in mind that these are actually extended IDs.

5:00Meaning that the actual ID, the element ID field

5:03is going to be populated with 255 or both

5:06of these information elements.

5:08And so we should absolutely keep in mind

5:09that 255 is going to be in the actual element ID field.

5:13But we should understand that 35 and 36

5:16are what's going to show up in the extended ID field.

5:19And by the way, when we map this out,

5:21this field is actually going to be separated by the length

5:23field here in the middle.

5:25So we've got the element ID here,

5:27and then we've got the extended ID over here on the right.

5:30So the length is going to be in the middle.

5:32However, that's fine, because we know

5:34that if 255 is listed here, then we're going to read the length

5:37and then we're going to get the actual extended ID

5:40at that point in the field that follows.

5:42Now lastly, we have SSID here at the bottom.

5:45Remember we said that this information

5:47element is the one that has the honor of having

5:49element ID of zero.

5:51And I suppose that's just because SSIDs

5:53are such a foundational part of all

5:54of this that they were given the first information element ID.

5:57And remember those are going to be included,

6:00especially in our probe requests, and responses,

6:03and beacons.

6:03So with that, our review of this skill and even

6:06some previous skills is over.

6:08If you find you couldn't quite identify all of the answers

6:10to some of these questions, then be sure to go back

6:12and review the materials.

6:13Whatever it takes to seal off those knowledge gaps.

6:15Otherwise, congratulations on completing

6:17Describe 802.11 HE Information Elements.

6:20I hope this has been informative for you.

6:22And I'd like to thank you for viewing.